Robotic positioning machines typically incorporate an articulated arm which moves throughout a defined volume for handling and assembling parts of various devices. These machines are used for various purposes, such as automatic assembly and numerically controlled machining, among others. Increasingly, such machines are placed under the control of a device such as a digital computer which controls the position and orientation of a manipulator element affixed to the arm. Examples of such machines are shown in U.S. Pat. No. 3,985,238 issued Oct. 12, 1976 to K. Nakura, et al and U.S Pat. No. 4,068,536 issued Jan. 17, 1978 to T. H. Stackhaus. These manipulators are essentially cantilevered arms incorporating a number of articulated and sliding joints to provide the requisite motion in space.
Among some of the more important characteristics of such machines are their load carrying capacity, their maximum operating speed (which, in large part, is a function of the inertia of the machine), and the simplicity of the machine, which not only affects its ease of use but also directly affects its cost. The load carrying capacity of many of the manipulators currently available, particularly those of the cantilevered arm type, are frequently quite limited in relation to the mass of the manipulator itself. Further, the construction of these manipulators is such as to create high translational and rotational moments of inertia with the result that the acceleration of the manipulator head, and thus the maximum speed of the manipulator itself, is unnecessarily limited. Further, their complexity frequently results in high cost, diminished reliability and consequent greater "down-time", and frequently an increased complexity of the control system for driving these machines.